Not only did FDR know exactly when the Japanese were on their way to Pearl Harbor, he may have conspired with Winston Churchill to lure (through boycotts of vital materials) the Japanese into the attack in order to get the USA into the war in Europe. This is exposed in the book "Day of Deceit: The Truth about FDR and Pearl Harbor" by Robert Stennett (2001). I'm sure Stennett is long dead but even while still reading his then new book, I found his telephone number in Oakland, California, called him and damn if he didn't pick-up.
The attack couldn't have been more timely. The Germans were at the gates of Moscow that December 1941. They could see the spires of the Kremlin. With Russia knocked out of the war, the fighting would have lasted much longer and far more costlier than it did.
And what did the USA lose but a few thousand dead, a few OLD battleships sunk, etc. All the new aircraft carriers were conveniently out-to-sea. And the Japanese didn't bomb any of the vital fuel "tank farms" at Pearl Harbor. They went after the "prize" ships that were lined up like sitting ducks. Obviously their intel was poor. Japanese fascist gangstas were high on easy victories in China and really screwed up at Pearl Harbor. One day US fascist gangstas will get carried away with themselves and screw-up big time. One more assassination or 9/11, and they may be toast--let us pray.
Within six months of the attack on Pearl Harbor, the US Navy slammed the Japanese Navy at Coral Sea and Midway. The first battle in May 1942 may have been a tie but the second the next month was a total victory.
Yes, as you can tell, the "sneak" attack on Pearl Harbor has long festered in my gut.
Thanks for reminding me. We are Historians Without Borders, correcting major falsehoods that have harmed millions. 2016 is our year to clean the slate.
Love heals . . .